Surface modification for interface stability in solid-state Li batteries

Chih-Chieh Wang^1*

¹Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan

* Presenter:Chih-Chieh Wang, email:chihcwang@mail.nsysu.edu.tw

Garnet type Li7La3Zr2O12 (LLZO) and NASICON type Li1.3Al0.3Ti1.7(PO4)3 (LATP) are promising solid state electrolytes (SSE) for lithium ion battery due to their excellent ion conductivity, chemical stability and wide electrochemical windows. However, several challenges must be addressed for practical applications. For instance, the formation of lithium carbonate leads to poor wettability of LLZO with lithium, resulting in increased interfacial resistance. Additionally, surface of LATP is unstable when in contact with Li metal because of the reduction reaction involving Ti4+, which adversely affects cycling performance. Both SSE also experience Li dendrite growth, attributed to a high electrical conductivity of grain boundary.
In this study, atomic layer deposition (ALD) is employed for surface modification of LLZO and LATP SSE. Unlike conventional method like CVD and PVD, ALD offers advantages like excellent step coverage, conformality and precise thickness control in nanoscale. By leveraging these advantages, the surface modification of LLZO and LATP using ALD results in a stable, well-wetting and dense surface, thereby reducing the interfacial resistance and enhancing cycling performances. For Al2O3 coated LLZO SSE, as the cycle number of ALD Al2O3 increases to 100, the conductivity improves from 2."59×10-4" to 8.26"×10-4" Scm-1. Compared to bare LLZO, the coted LLZO samples demonstrate more stable galvanostatic cycling, likely due to the segregation of aluminum at the grain boundary. For 50 cycles of ALD ZnO coated LATP SSE, the voltage during lithium stripping and plating cycling remains stable at ~ 1.30 V for 100 cycles, exhibiting a consistent voltage gap. These results suggest that the growth of lithium dendrite can be effectively suppressed by ALD ZnO coating.

Keywords: solid state electrolyte, atomic layer deposition, lithium battery, LLZO, LATP